JP7164344B2 - Oxidation-reduction potential determination device, desulfurization device provided with the same, and oxidation-reduction potential determination method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxidation-reduction potential determination device, a desulfurization device including the same, and an oxidation-reduction potential determination method.

Various mercury removal processes have been developed for the purpose of controlling mercury emissions from thermal power plants to the atmosphere. For example, in a flue gas treatment system having a boiler, a denitrification device, an electrostatic precipitator, a desulfurization device, etc., mercury is oxidized into easily soluble divalent mercury (Hg ²⁺ ) in the denitrification device and captured by the absorbent of the wet desulfurization device. process is known.

FIG. 8 is a diagram for explaining the concept of mercury removal in the exhaust gas treatment system 100 including the conventional desulfurization device 110. As shown in FIG. FIG. 8 is a diagram for explaining the technology described in Patent Document 1 (especially see FIG. 1 of Patent Document 1). The flue gas treatment system 100 treats flue gas generated by combustion of fuel in the boiler 111 . The fuel here is, for example, heavy oil, which contains sulfur, nitrogen, mercury and the like.

Combustion gas is generated when the fuel is combusted in the internal space 111a of the boiler 111 . At this time, the sulfur content in the fuel is contained in the combustion gas as sulfur oxides, the nitrogen content in the fuel as nitrogen oxides, and the mercury vaporizes as gaseous mercury. Further, in the boiler 111, combustion ash is generated along with the generation of combustion gas.

The generated combustion gas is supplied to the reduction type denitrification device 112 as combustion exhaust gas. The denitrification device 112 removes the nitrogen content (nitrogen oxides) in the flue gas. Further, in the denitrification device 112, the metallic mercury (Hg ⁰ ) contained in the combustion exhaust gas is oxidized to generate divalent mercury (Hg ²⁺ ). Therefore, the flue gas supplied to the subsequent dust collector 113 and the like contains divalent mercury. Next, in the dust collector 113 (electric dust collector), combustion ash contained in the combustion exhaust gas is removed. Here, part of the mercury in the flue gas is removed in a gaseous state in the dust collector 113 along with the combustion ash. Then, the flue gas from which the nitrogen content, combustion ash and part of the mercury have been removed is supplied to the desulfurization device 110 .

The desulfurization device 110 is, for example, a desulfurization device based on a wet lime-gypsum method, and is for removing sulfur content in the flue gas by bringing the flue gas into contact with an absorbent. When the absorbent is, for example, lime water (slurry containing calcium carbonate), contacting the flue gas with the absorbent causes reaction formulas (1) and (2) below.

Reaction formula (1):
SO2 _{+ CaCO3} +1/2H2O→ _CaSO3.1 / _{2H2O + CO2}
Reaction formula (2):
CaSO3.1/2H2O _{+ 3} /2H2O _{+ 1} / _2O2 → _CaSO4.2H2O

As shown in reaction formulas (1) and (2), sulfur dioxide (sulfur oxides) in the flue gas reacts with calcium carbonate in the absorbent to form calcium sulfate (gypsum) via calcium sulfite. Generate. Since calcium sulfate is sparingly soluble in water, by doing so, the sulfur content in the flue gas can be separated from the absorbent as a solid phase.

The desulfurization device 110 comprises a housing 3 having an interior space 3a for taking in flue gas. The housing 3 is provided with an inlet 1 for taking combustion exhaust gas into the internal space 3a and an outlet 2 for discharging purified gas (combustion exhaust gas after removing sulfur content) from the internal space 3a to the outside. . The desulfurization device 110 also includes a water sprinkler 4 for watering the internal space 3a with an absorption liquid for absorbing sulfur content. The sprinkler device 4 is arranged to extend horizontally between the inlet 1 and the outlet 2 in the height direction.

The water sprinkler 4 has a hole (not shown) that opens upward, and the absorption liquid is watered upward through the hole. Therefore, the combustion exhaust gas flowing upward from the inflow port 1 to the outflow port 2 and the absorbing liquid, which is also sprayed upward, come into contact with each other in the internal space 3a. As a result, the sulfur content in the combustion exhaust gas is absorbed and removed by the absorbent, and the combustion exhaust gas from which the sulfur content has been removed, that is, the purified gas is discharged from the outflow port 2 . The exhausted purge gas is discharged to the atmosphere through chimney 114 .

The desulfurization apparatus 110 also includes a circulation system 11 for circulating the absorbent by supplying the absorbent staying at the bottom of the housing 3 to the sprinkler 4, and a pump 6 for flowing the absorbent in the circulation system 11. and In the desulfurization device 110 , part of the circulating liquid remaining in the bottom of the housing 3 is extracted through the circulation system 11 , and the extracted absorbing liquid is sprinkled into the internal space 3 a by the sprinkler device 4 .

The circulation system 11 is connected to an extraction system 12 for extracting from the circulation system 11 a portion of the absorbent staying at the bottom of the housing 3 . A solid-liquid separator 7 is connected to the extraction system 12 . The solid-liquid separator 7 separates gypsum as a solid phase. On the other hand, since mercury (divalent mercury) that has not adhered to the gypsum may remain in the liquid as the liquid phase remaining in the solid-liquid separator 7, the liquid may also contain mercury (divalent mercury). Therefore, the liquid is subjected to mercury removal treatment in the wastewater treatment device 115, for example, by using a chelating agent. Then, the liquid after removing the mercury is drained to the outside.

In the exhaust gas treatment system 100, the oxidation-reduction potential (hereinafter referred to as ORP) of the absorbent staying at the bottom of the housing 3 is measured. The ORP is measured using a sensor section 109 a that is placed in the absorption liquid at the bottom of the housing 3 and connected to the ORP meter 109 . The reduction of divalent mercury is suppressed by supplying the oxidizing agent to the absorbing liquid so that the ORP of the absorbing liquid staying at the bottom of the housing 3 is within a predetermined range. As a result, re-scattering of mercury from the absorbing liquid to the purified gas is suppressed.

As described above, mercury is separated from the flue gas together with combustion ash by the dust collector 113 in the front stage of the desulfurization device 110 , and is also separated from the flue gas in the desulfurization device 110 . That is, when the wet lime-gypsum method is used for the desulfurization apparatus 110, the mercury absorbed by the absorbing liquid is mainly discharged outside the system through the following three routes.

The first route is the solid phase (gypsum), and mercury is discharged in a form stabilized in the solid phase produced by the desulfurization reaction. The second is the liquid phase (liquid), and mercury is discharged in a dissolved state in the liquid phase. Thirdly, mercury is discharged into the gas phase in a state of being mixed with the purification gas, although the technique described in Patent Document 1 is intended to suppress it. Of these, the third route is the release of mercury into the gas phase. I can say.

JP 2013-6144 A

By the way, in FIG. 8, the amount of mercury per absorbing liquid volume existing in the liquid phase portion of the absorbing liquid in the desulfurization apparatus 110 is referred to as "liquid phase mercury concentration". In addition, the amount of mercury contained in the solid phase portion of the absorbent, specifically the residue (mainly gypsum) after filtration of the absorbent, per volume of the absorbent is referred to as "solid-phase mercury concentration". Also, the amount of mercury per absorption liquid volume is referred to as "total mercury concentration". The total mercury concentration is equal to the sum of the liquid phase mercury concentration and the solid phase mercury concentration. Then, the "liquid phase mercury ratio" is calculated by dividing the liquid phase mercury concentration by the total mercury concentration. Similarly, by dividing the solid-phase mercury concentration by the total mercury concentration, the "solid-phase mercury ratio" is calculated.
These terms also have the same meanings in the desulfurization apparatus described below.

In a general desulfurization apparatus, the liquid-phase mercury proportion and the solid-phase mercury proportion are naturally determined depending on the operating conditions of the plant including the desulfurization apparatus. Therefore, depending on the operating conditions of the plant, there is a possibility that mercury cannot be discharged through the route desired by the manager or the like. As a specific problem that can occur, if the liquid phase mercury ratio becomes excessive, mercury cannot be sufficiently removed even if wastewater treatment equipment is installed, and there is a possibility that it will conflict with the regulation value for wastewater mercury concentration. On the other hand, if the solid-phase mercury ratio is too high, the mercury concentration may exceed the standard value for gypsum trade, making it difficult to reuse gypsum.

Therefore, it is preferable that the liquid-phase mercury ratio and the solid-phase mercury ratio can be arbitrarily changed according to a request from a manager or the like. However, Patent Document 1 only describes suppression of re-entrainment of mercury from the absorbing liquid to the purification gas, and does not describe a method for arbitrarily changing the liquid phase mercury proportion and the solid phase mercury proportion.

An object of at least one embodiment of the present invention is to provide an oxidation-reduction potential determining apparatus capable of arbitrarily changing the liquid-phase mercury proportion and the solid-phase mercury proportion, a desulfurization apparatus including the same, and an oxidation-reduction potential determining method. .

(1) An oxidation-reduction potential determination device according to at least one embodiment of the present invention,
An oxidation-reduction potential determining device for determining the operating oxidation-reduction potential of the absorbing liquid in a desulfurization apparatus having a space inside for desulfurizing combustion exhaust gas containing sulfur and mercury by contact with the absorbing liquid, ,
The oxidation-reduction potential determination device comprises:
a target value for one of the liquid-phase mercury ratio and the solid-phase mercury ratio in the absorbing liquid;
a predetermined correlation that is a correlation between the mercury ratio and the oxidation-reduction potential of the absorbing liquid;
and an operating oxidation-reduction potential determination unit for determining the operating value of the oxidation-reduction potential based on the above and arbitrarily changing the mercury proportion .

According to the configuration (1) above, the mercury ratio can be arbitrarily changed by controlling the oxidation-reduction potential of the absorbing liquid. As a result, the mercury concentration can be controlled to the target value required by the administrator or the like.

(2) In some embodiments, in the configuration of (1) above,
The oxidation-reduction potential determination device determines the target value of the mercury ratio based on the inflow mercury concentration to the desulfurization device and the target value of one of the liquid-phase mercury concentration and the solid-phase mercury concentration. It is characterized by comprising a target mercury ratio determination unit for determination.

According to the above configuration (2), one of the liquid-phase mercury concentration and the solid-phase mercury concentration can be controlled to a target value required by an administrator or the like.

(3) In some embodiments, in the configuration of (2) above,
The target mercury ratio determining unit is further configured to determine the target value of the mercury ratio based on operating conditions of the desulfurization apparatus.

According to the above configuration (3), even if the mercury ratio fluctuates due to a change in the operating conditions of the desulfurization apparatus even though the operating oxidation-reduction potential is not changed, the mercury concentration is kept at the target value. You can control it.

(4) A desulfurization device according to at least one embodiment of the present invention, the oxidation-reduction potential determination device according to any one of (1) to (3) above;
a supply device for supplying at least one of air and a redox agent to the absorption liquid;
The supply device is configured to supply at least one of the air and the oxidation-reduction agent so as to achieve the operating oxidation-reduction potential determined by the oxidation-reduction potential determination device.

According to the above configuration (4), the ORP of the absorbing liquid can be controlled by controlling the supply amount of at least one of the air and the redox agent. As a result, one of the liquid phase mercury proportion and the solid phase mercury proportion can be controlled to the target value required by the manager or the like.

(5) In some embodiments, in the configuration of (4) above,
The supply device is configured to supply at least one of the air and the redox agent when the concentration of mercury flowing into the desulfurization device exceeds a predetermined threshold.

According to the configuration (5) above, control is not performed when the concentration of inflowing mercury is low, so the computational load of the oxidation-reduction potential determination device can be reduced.

(6) The oxidation-reduction potential determination method according to at least one embodiment of the present invention comprises
An oxidation-reduction potential determination method for determining the operating oxidation-reduction potential of an absorption liquid in a desulfurization apparatus having a space inside for desulfurizing combustion exhaust gas containing sulfur and mercury by contact with the absorption liquid, ,
The oxidation-reduction potential determination method includes:
a target value for one of the liquid-phase mercury ratio and the solid-phase mercury ratio in the absorbing liquid;
a predetermined correlation that is a correlation between the mercury ratio and the oxidation-reduction potential of the absorbing liquid;
and an operating redox potential determination step of determining an operating value of the operating redox potential based on and optionally changing the mercury ratio .

According to the above method (6), the mercury ratio can be arbitrarily changed by controlling the oxidation-reduction potential of the absorbing solution, thereby controlling the mercury concentration to the target value required by the manager or the like.

According to at least one embodiment of the present invention, it is possible to provide an oxidation-reduction potential determination device capable of arbitrarily changing the liquid-phase mercury proportion and the solid-phase mercury proportion, a desulfurization device including the same, and an oxidation-reduction potential determination method. .

BRIEF DESCRIPTION OF THE DRAWINGS It is a system diagram which shows the desulfurization apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the definition of the term regarding mercury. It is a figure which shows the structure of an ORP meter. It is a block diagram of an arithmetic control unit. It is a correlation between the ORP of the absorbing liquid and the liquid phase mercury ratio. It is a graph which shows the liquid phase mercury ratio with respect to ORP of an absorption liquid, and is a graph obtained by plotting the experimental result obtained by the present inventors. 4 is a flow chart showing a method for determining redox potential according to one embodiment of the present invention. FIG. 4 is a diagram for explaining the concept of mercury removal in an exhaust gas treatment system provided with a conventional desulfurization device.

Several embodiments of the present invention will now be described with reference to the accompanying drawings. However, the contents described as embodiments or the contents described in the drawings below are merely examples, and can be arbitrarily changed and implemented without departing from the scope of the present invention. Moreover, each embodiment can be implemented by combining two or more arbitrarily. Furthermore, in each embodiment, common members are denoted by the same reference numerals, and overlapping descriptions are omitted for simplification of description.

In addition, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. do not have.
For example, expressions denoting relative or absolute arrangements such as "in a direction", "along a direction", "parallel", "perpendicular", "center", "concentric" or "coaxial" are strictly not only represents such an arrangement, but also represents a state of relative displacement with a tolerance or an angle or distance to the extent that the same function can be obtained.
For example, expressions such as "identical", "equal", and "homogeneous", which express that things are in the same state, not only express the state of being strictly equal, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the existing state.
For example, expressions that express shapes such as squares and cylinders do not only represent shapes such as squares and cylinders in a geometrically strict sense, but also include irregularities and chamfers to the extent that the same effect can be obtained. The shape including the part etc. shall also be represented.
On the other hand, the expressions "comprising", "comprising", "having", "including", or "having" one component are not exclusive expressions excluding the presence of other components.

FIG. 1 is a system diagram showing a desulfurization device 10 according to one embodiment of the present invention. The desulfurization device 10 can be applied, for example, in place of the desulfurization device 110 shown in FIG. The desulfurization device 10 has therein a space (internal space 3a) for desulfurizing flue gas containing sulfur and mercury by contact with an absorbent. The sulfur content here includes sulfur oxides such as sulfur monoxide and sulfur dioxide. Mercury is also contained as gaseous mercury in the flue gas.

FIG. 2 is a diagram for explaining definitions of terms related to mercury. Total mercury consists of liquid phase mercury (Hg ²⁺ (liquid l)) and solid phase mercury (HgX (solid s)). Liquid phase mercury includes, for example, mercury chloride and mercury hydroxide. Solid-phase mercury, on the other hand, includes sparingly soluble compounds represented, for example, by the formula HgX, where X is one or more elements forming anions. Solid phase mercury is usually present in the absorption liquid by adhering to the gypsum.

Although the details will be described later, the absorption liquid absorbs mercury (bivalent mercury (Hg ²⁺ )) together with the sulfur content. The absorbed mercury forms, for example, together with anions, the sparingly soluble compounds mentioned above and precipitates. The precipitated poorly soluble compound adheres to the gypsum and exists as solid phase mercury in the absorption solution. On the other hand, mercury that remains in the liquid as divalent mercury after being absorbed by the absorbing liquid is called liquid phase mercury. Liquid-phase mercury also includes bivalent mercury that is generated in a liquid by dissolving the once-generated solid-phase mercury.

Liquid-phase mercury and solid-phase mercury can be separated by solid-liquid separation of the absorption liquid by the solid-liquid separator 7 . At this time, solid-phase mercury is contained in the separated gypsum. Furthermore, the concentrations of liquid-phase mercury and solid-phase mercury are measured for each of the liquid phase (solution) and solid phase (gypsum) separated by the solid-liquid separator 7 using, for example, an inductively coupled plasma mass spectrometer. can.

Returning to FIG. 1, the desulfurization apparatus 10 performs desulfurization by, for example, the lime-gypsum method (wet type), and the absorbent is, for example, lime water (calcium carbonate slurry). The desulfurization apparatus 10 can adopt a system such as a spray system or a grid system in addition to the liquid column system shown in FIG.

The desulfurization apparatus 10 includes a housing 3 having an inlet 1 for flue gas, an outlet 2 for purified gas from which sulfur and mercury have been removed, and an internal space 3a in which the flue gas and an absorbent are brought into contact with each other. and The desulfurization apparatus 10 also includes a sprinkler device 4 (for example, a sprinkler nozzle, or a tray such as a perforated plate) for sprinkling the absorbent inside the housing 3, and a diffuser for diffusing air into the absorbent. a trachea 5; Air is supplied to the absorbing liquid through the diffuser tube 5 through an air supply system 15 .

The amount of air supplied to the absorbent is controlled by controlling the rotational speed of the pump 21 (supply device) provided in the air supply system 15 . The air supply amount is controlled by providing an opening adjustment bubble in the air supply system 15, controlling the opening of the valve, controlling the number of pumps 6 to be driven, and providing a branch line that is open to the atmosphere in the air supply system 15. Moreover, it can also be carried out by adjusting the opening degree of a valve provided on the branch line.

Any oxidizing agent may be used in place of or in addition to air. In this case, depending on the state of the oxidant (gas, liquid, or solid), it can be diffused or added to the absorption liquid.

The oxidizing agent supplied to the absorption liquid may be any oxidizing agent such as sodium hypochlorite, potassium peroxodisulfate, hydrogen peroxide, together with or instead of the air. Furthermore, in order to control the oxidation-reduction potential of the absorption liquid (described later), the absorption liquid may optionally contain an optional reducing agent (oxidation-reduction form of agent) may be provided. Examples of reducing agents that can be used include sodium thiosulfate, sodium metabisulfite, sodium sulfide, sodium hydrogensulfide, and the like. The pump 21 (supply device) is therefore for supplying at least one of air and redox agent to the absorption liquid.

The desulfurization apparatus 10 also includes a circulation system 11 for circulating the absorbent by sprinkling the absorbent staying at the bottom of the housing 3 from the sprinkler 4, and a pump for circulating the absorbent in the circulation system 11. 6. A withdrawal system 12 is connected to the circulation system 11 , and a solid-liquid separator 7 is connected to the withdrawal system 12 . A part of the absorbent flowing through the circulation system 11 flows through the extraction system 12 and is supplied to the solid-liquid separator 7 . The solid-liquid separator 7 is, for example, a belt filter, in which the solid phase in the absorbing liquid generated by contact with the combustion exhaust gas is separated. The separated solid phase is discharged outside through the gypsum system 13 as gypsum.

The liquid phase remaining after the solid phase is separated in the solid-liquid separator 7 flows again through the extraction system 12 and is returned to the housing 3 again. At this time, part of the liquid phase is discharged to the outside through the drainage system 14 .

The withdrawal system 12 is equipped with an ORP meter 8 for measuring the ORP of the absorbent and a pH meter 9 for measuring the pH of the absorbent. The ORP and pH to be measured are those of the liquid phase of the absorbing liquid, but since the ORP and pH of the absorbing liquid are the same regardless of the presence or absence of the solid phase, in one embodiment of the present invention, the liquid phase are used as the ORP and pH of the absorption solution. The measured ORP and pH of the absorbing liquid are input to the arithmetic control unit 50 .

The absorbent measured here is sprinkled into the internal space 3 a of the housing 3 through the absorbent reservoir at the bottom of the housing 3 , the circulation system 11 and the sprinkler 4 . Therefore, the ORP and pH measured here become the ORP and pH of the absorbing liquid to be brought into contact with the flue gas.

The configuration of the ORP meter 8 will be described.
FIG. 3 is a diagram showing the structure of the ORP meter 8. As shown in FIG. The ORP meter 8 is placed in the extraction system 12 as described above. More specifically, the ORP meter 8 is arranged on the wall portion 8b of the pipe 8a that constitutes the extraction system 12 .

Circular openings 101 and 105 are formed in the wall portion 8b of the pipe 8a. In the opening 101, a reference electrode 102 having a silver chloride film formed by chlorinating the silver wire surface is arranged so as to penetrate the wall portion 8b of the pipe 8a. A reference electrode 102 is fixed to the wall portion 8 b via an insulator 103 fitted in the opening 101 . The reference electrode 102 is connected to a lead wire 104 that is connected to an arithmetic control unit 50 (not shown in FIG. 3). Therefore, the potential measured by the reference electrode 102 is output to the arithmetic control device 50 .

An indicator electrode 106 made of platinum is arranged in the opening 105 so as to penetrate the wall 8b of the pipe 8a. The indicator electrode 106 is fixed to the wall 8b via an insulator 107 fitted in the opening 105. As shown in FIG. The indicator electrode 106 is connected to a lead wire 108 that is connected to an arithmetic control unit 50 (not shown in FIG. 3). Therefore, the potential measured by indicator electrode 106 is output to arithmetic and control unit 50 .

Based on the potential of the reference electrode 102 and the potential of the indicator electrode 106, the arithmetic control unit 50 measures the ORP of the absorbent flowing through the pipe 8a (that is, the ORP of the absorbent flowing through the extraction system 12). In the example shown in FIG. 3, the position of the reference electrode 102 and the position of the indicator electrode 106 may be reversed. Also, a composite electrode in which the reference electrode 102 and the indicator electrode 106 are integrated may be used. Although the ORP meter 8 is directly arranged in the pipe 110 in FIG. 3, it may be inserted into a separately provided tank (not shown). Also, it does not matter whether the tank is open to the atmosphere.

Returning to FIG. 1, the arithmetic control device 50 (oxidation-reduction potential determining device) is for determining the operation ORP of the absorbent. The arithmetic and control unit 50 will be described with reference to FIG.

FIG. 4 is a block diagram of the arithmetic and control unit 50. As shown in FIG. Mercury (divalent mercury) contained in the flue gas is absorbed by the absorbent upon contact with the absorbent. Then, whether the absorbed mercury moves to the liquid phase or the solid phase of the absorbing liquid is determined by the ORP of the absorbing liquid when it comes into contact with the flue gas. The liquid phase mercury described with reference to FIG. 2 above corresponds to mercury that has transitioned to the liquid phase, and the solid phase mercury described with reference to FIG. 2 above corresponds to mercury that has transitioned to the solid phase. do.

The arithmetic control unit 50 includes an input unit 51 , an inflow divalent mercury concentration determination unit 52 , a target liquid phase mercury ratio determination unit 53 , an operation ORP determination unit 54 , a control unit 55 and a correlation 56 .

The input unit 51 is for inputting a target value of liquid-phase mercury concentration (control value of mercury concentration in wastewater). The target value referred to here may be a single value, or may be, for example, a range of a predetermined value or more and a predetermined value or less. Although the details will be described later, the target value of the liquid phase mercury ratio is determined based on the inputted target value. Note that the input unit 51 is composed of, for example, a keyboard, a mouse, a numeric keypad, and the like.

Note that the target value of the solid-phase mercury concentration may be input to the input unit 51 instead of the target value of the liquid-phase mercury concentration. Therefore, the input unit 51 receives one of the liquid-phase mercury concentration target value and the solid-phase mercury concentration target value.

The inflow divalent mercury concentration determination unit 52 is for determining the divalent mercury (Hg ²⁺ ) concentration flowing into the desulfurization apparatus 10 . That is, the inflow divalent mercury concentration determining unit 52 determines the concentration of divalent mercury contained in the flue gas that flows in through the inlet 1 of the desulfurization device 10 . As described above, divalent mercury is generated by oxidation of metallic mercury in, for example, a reduction-type denitrification device (not shown; any other reduction device may be used) provided upstream of the desulfurization device 10.

A specific method for determining the concentration of divalent mercury in the flue gas is not particularly limited. It can be determined based on the equipment configuration on the upstream side of the desulfurization device 10 . Further, for example, the flue gas flowing into the desulfurization apparatus 10 can also be determined using, for example, a continuous mercury analyzer. Furthermore, for example, a portion of the combustion exhaust gas may be sampled and determined by manual analysis using an arbitrary analyzer. In this case, the determined divalent mercury concentration can be input to the inflow divalent mercury concentration determination unit 52 by being input through the input unit 51, for example.

The target liquid phase mercury ratio determination unit 53 (target mercury ratio determination unit) determines the target mercury concentration based on the inflow mercury concentration to the desulfurization apparatus 10 and the target value of either the liquid phase mercury concentration or the solid phase mercury concentration. , to determine the target value for the percentage of mercury. Specifically, in one embodiment of the present invention, the target liquid phase mercury ratio determining unit 53 determines the concentration of divalent mercury input to the inflowing divalent mercury concentration determining unit 52 and the amount of flue gas flowing into the desulfurization apparatus 10. It is for determining the target value of the liquid phase mercury ratio from the flow rate, the circulating flow rate of the absorbent in the desulfurization apparatus 10 and the target value of the liquid phase mercury concentration input by the input unit 51 . Specifically, for example, when the divalent mercury concentration flowing into the absorbing solution is 100 µg/L in terms of the concentration of the absorbing solution, and the target value of the liquid-phase mercury concentration (control value for mercury concentration in wastewater) is 10 µg/L. , the target value of the target liquid phase mercury proportion is 10/100=0.1 [-].

When the target value of the solid-phase mercury concentration is input to the input unit 51, a target solid-phase mercury ratio determination unit (target mercury ratio determination unit) (not shown) inputs to the inflow divalent mercury concentration determination unit 52. from the obtained divalent mercury concentration, the flow rate of the flue gas flowing into the desulfurization apparatus 10, the circulation flow rate of the absorbent in the desulfurization apparatus 10, and the target value of the solid-phase mercury concentration input at the input unit 51, A target value for the mercury percentage may be determined. That is, the target mercury ratio determination unit (not shown) determines the divalent mercury concentration input to the inflow divalent mercury concentration determination unit 52, the flow rate of the flue gas flowing into the desulfurization device 10, and the circulation flow rate of the absorbent in the desulfurization device 10. and a target value of one of the liquid phase mercury concentration and the solid phase mercury concentration, the target value of the mercury proportion is determined. As a result, one of the liquid-phase mercury concentration and the solid-phase mercury concentration can be controlled to the target value required by the administrator or the like.

Further, the target liquid-phase mercury ratio determination unit 53 (target mercury ratio determination unit) is further configured to determine the target value of the mercury ratio based on the operating conditions of the desulfurization apparatus 10 . Specifically, for example, the operating condition is, for example, the concentration of sulfur dioxide in the inflowing flue gas (that is, the inlet concentration of sulfur dioxide). Further, for example, depending on the composition of the absorbing liquid, the correlation 56 (described later) between the liquid mercury concentration and the ORP may change. Therefore, by determining the target value of the mercury ratio based on the operating conditions of the desulfurization device 10, even if the operating ORP is not changed due to changes in the operating conditions of the desulfurization device 10, However, the mercury concentration can be controlled to the target value.

The operation ORP determination unit 54 determines the operation of the ORP based on the target value of the liquid phase mercury proportion in the absorbing liquid and the predetermined correlation 56 that is the correlation 56 between the liquid phase mercury proportion and the ORP of the absorbing liquid. It is for determining the value. However, when the solid-phase mercury concentration is input to the input unit 51, the operation ORP determination unit 54 determines the target value of the solid-phase mercury ratio in the absorbing solution, the solid-phase mercury ratio, and the ORP of the absorbing solution. Based on the correlation 56 and the predetermined correlation 56, an operating value of ORP may be determined.

Therefore, the operating ORP determination unit 54 determines a target value of one of the liquid-phase mercury ratio and the solid-phase mercury ratio in the absorbent, and the correlation between the mercury ratio and the ORP of the absorbent, which is predetermined. determining an operating value of ORP based on the correlation; By providing the operation ORP determination unit 54, the mercury ratio can be arbitrarily changed by the ORP control of the absorbent, thereby controlling the mercury ratio to the target value required by the manager or the like.

As a result of conducting various experiments, the inventors found that the oxidation-reduction potential (ORP) of the absorbing liquid and the liquid phase mercury ratio in the absorbing liquid show a good correlation as shown in FIG. It has arrived.
Correlation 56 is described with reference to FIG.
FIG. 5 is a correlation 56 between the ORP of the absorbing solution and the liquid phase mercury fraction. A graph showing the correlation 56 is determined in advance by, for example, a test at the design stage, a test run of the desulfurization apparatus 10, or the like, and stored in advance in the arithmetic and control unit 50. FIG. For example, when the administrator or the like of the desulfurization apparatus 10 inputs through the input unit 51 that "the target value of liquid phase mercury concentration (control value of mercury concentration in waste water) is 10 μg/L or less", the inflow divalent mercury concentration is 100 μg/L, the target liquid phase mercury proportion is 0.1 or less. Therefore, the operation ORP determining unit 54 determines the ORP of the absorbent corresponding to the liquid phase mercury ratio of 0.1 based on the correlation 56 . In this case, the ORP of the absorbent to be brought into contact with the combustion exhaust gas is controlled by the control unit 55 described later so that the ORP value x1 or less is determined here.
Note that the correlation 56 stored in the arithmetic and control unit 50 does not have to be a graph, and may be, for example, an approximation formula, a table, or the like.

FIG. 6 is a graph showing the ratio of liquid phase mercury to the ORP of the absorbing liquid, and is a graph obtained by plotting the experimental results obtained by the present inventors. As shown in FIG. 6, when the ORP (horizontal axis) of the absorbing liquid is approximately 300 mV or less, the liquid phase mercury ratio (vertical axis) is 0.3 or less. Therefore, when the ORP is approximately 300 mV or less, the liquid phase mercury concentration is relatively low and the solid phase mercury concentration is relatively high. On the other hand, when the ORP of the absorbing liquid is approximately 300 mV or more, the liquid phase mercury ratio is approximately 0.3 or more. Therefore, when the ORP is about 300 mV or more, the liquid phase mercury concentration is relatively high and the solid phase mercury concentration is relatively low.

As shown in FIG. 6, as a result of examination by the present inventors, it was found that there is a correlation between the ORP of the absorbing solution and the liquid phase mercury ratio. Therefore, in one embodiment of the present invention, an approximate curve is determined based on the graph of FIG. 6, and the determined approximate curve is used as the correlation 56 shown in FIG.

5 and 6 show the correlation between the ORP and the liquid-phase mercury ratio as an example, but the correlation between the ORP and the solid-phase mercury ratio is similar based on, for example, tests at the design stage. can be determined to

Returning to FIG. 4, the control unit 55 controls the air amount to the absorbent so that the operation ORP determined by the operation ORP determination unit 54 is obtained. Specifically, as described above, the amount of air supply is controlled by controlling the rotation speed of the pump 21 by the control unit 55, for example. That is, the pump 21 is configured to supply air so as to achieve the operation ORP determined by the operation ORP determination unit 54 . This makes it possible to control the ORP of the absorbent that is sprayed via the circulation system 11 and the sprinkler 4 and brought into contact with the flue gas.

The controller 55 can control the amount of air while monitoring the ORP of the absorbent using the ORP meter 8, for example. In addition, the ORP may be controlled using a redox agent in combination, if necessary. Therefore, the pump 21 (supply device, see FIG. 1) is designed to supply at least one of the air and the redox agent so as to achieve the operating ORP determined by the arithmetic control device 50 (redox potential determination device). configured to By doing so, the ORP of the absorbent can be controlled by controlling the supply amount of at least one of the air and the redox agent. As a result, one of the liquid phase mercury proportion and the solid phase mercury proportion can be adjusted to control the mercury concentration to the target value required by the manager or the like.

Further, in one embodiment of the present invention, the pump 21 (supply device) supplies air or a redox agent when the inflow divalent mercury concentration (inflow mercury concentration) into the desulfurization device 10 exceeds a predetermined threshold value. is configured to supply at least one of By doing so, control is not performed when the concentration of inflowing divalent mercury is low, so the calculation load of the arithmetic control device 50 (oxidation-reduction potential determination device) can be reduced.

Although not shown, the arithmetic and control unit 50 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), and an I/F (Interface). , a control circuit, etc., and is embodied by the CPU executing a predetermined control program stored in the ROM.

FIG. 7 is a flowchart illustrating an ORP determination method according to one embodiment of the present invention. The flow shown in FIG. 7 is performed by the arithmetic and control unit 50 (see FIGS. 1 and 2). Therefore, FIG. 7 will be described with reference to FIGS. 1 and 2 as appropriate.

First, for example, when the target value of the liquid phase mercury concentration (control value of mercury concentration in waste water) is input to the input unit 51, the inflow divalent mercury concentration determining unit 52 determines the divalent mercury concentration flowing into the desulfurization apparatus 10. (step S1). The input unit 51 may be inputted with a target value of solid-phase mercury concentration (control value of mercury concentration in gypsum) instead of the target value of liquid-phase mercury concentration. Next, the target liquid phase mercury ratio determining unit 53 calculates an appropriate liquid phase mercury ratio from the desulfurization apparatus operating conditions and the target value (step S2).

Here, regarding the operating conditions of the desulfurization apparatus, if the operating conditions of the desulfurization apparatus change, there is a possibility that the liquid-phase mercury concentration and the solid-phase mercury concentration will change. Specifically, for example, when the amount of desulfurization increases, the amount of gypsum produced increases. Therefore, when the concentration of inflowing divalent mercury is constant and the proportion of liquid-phase mercury is constant, the solid-phase mercury concentration relatively decreases. Therefore, in one embodiment of the present invention, the target liquid-phase mercury proportion determining unit 53 further determines the target value of the liquid-phase mercury proportion based on the operating conditions of the desulfurization apparatus 10 .

Next, the operating ORP determining unit 54 determines the operating ORP from the calculated liquid phase mercury ratio and the ORP correlation 56 shown in FIG. 5 (step S3). Then, the control unit 55 controls the amount of air supplied to the desulfurization device 10 so as to achieve the determined operation ORP. As a result, the liquid phase mercury concentration becomes equal to or less than the target value (below the control value). Also, the operating ORP may be determined from the calculated solid-phase mercury ratio.

After the ORP of the absorbent is controlled, the target liquid phase mercury ratio determining unit 53 grasps the operating conditions of the desulfurization apparatus 10 and monitors whether or not the operating conditions have changed (step S4). If there is no change in the operating conditions (No direction), the inflow divalent mercury concentration determining unit 52 grasps the inflow divalent mercury concentration and monitors whether the inflow divalent mercury concentration has changed. (Step S5). When the concentration of inflowing divalent mercury has not changed (No direction) and the operation is to be continued (Yes direction of step S6), step S4 and subsequent steps are performed again. On the other hand, when the operation is not continued (No direction), the operation ends.

Further, if there is a change in the operating state in step S4 (Yes direction), step S2 and subsequent steps are repeated. Furthermore, in step S5 above, if the inflow concentration of mercury has changed (Yes direction), step S1 and subsequent steps are repeated.

According to the ORP determination method and the ORP control method including the above, the mercury ratio can be arbitrarily changed by the ORP control of the absorbent. As a result, the mercury concentration can be controlled to the target value required by the manager or the like.

1 Inlet 2 Outlet 3 Case 3a, 111a Interior space 4 Sprinkler 5 Air diffuser 6, 7, 21 Pump 7 Solid-liquid separator 8, 109 ORP meter 9 pH meter 8a Piping 8b Wall 10, 110 Desulfurization device 11 Circulation system 12 System 13 Gypsum system 14 Drainage system 15 Air supply system 50 Arithmetic control device 51 Input unit 52 Inflow divalent mercury concentration determination unit 53 Target liquid phase mercury ratio determination unit 54 Determination unit 55 Control unit 56 Correlation 100 Exhaust gas treatment system 101 , 105 opening 102 reference electrode 103, 107 insulator 104, 108 lead wire 106 indicator electrode 109a sensor unit 111 boiler 112 denitration device 113 dust collector 114 chimney 115 waste water treatment device

Claims (6)

An oxidation-reduction potential determining device for determining the operating oxidation-reduction potential of the absorbing liquid in a desulfurization apparatus having a space inside for desulfurizing combustion exhaust gas containing sulfur and mercury by contact with the absorbing liquid, ,
The oxidation-reduction potential determination device comprises:
a target value for one of the liquid-phase mercury ratio and the solid-phase mercury ratio in the absorbing liquid;
a predetermined correlation that is a correlation between the mercury ratio and the oxidation-reduction potential of the absorbing liquid;
and an operating oxidation-reduction potential determining unit for determining the operating value of the oxidation-reduction potential based on and optionally changing the mercury proportion . The oxidation-reduction potential determination device determines the target value of the mercury ratio based on the inflow mercury concentration to the desulfurization device and the target value of one of the liquid-phase mercury concentration and the solid-phase mercury concentration. 2. The oxidation-reduction potential determination device according to claim 1, further comprising a target mercury ratio determination unit for determination. 3. The oxidation-reduction potential according to claim 2, wherein the target mercury ratio determining unit is further configured to determine the target value of the mercury ratio based on operating conditions of the desulfurization apparatus. decision device. an oxidation-reduction potential determination device according to any one of claims 1 to 3;
a supply device for supplying at least one of air or a redox agent to the absorption liquid;
with
The supply device is configured to supply at least one of the air and the redox agent to the operating oxidation-reduction potential determined by the oxidation-reduction potential determination device, Desulfurization equipment. The supply device is configured to supply at least one of the air and the redox agent when the mercury concentration flowing into the desulfurization device exceeds a predetermined threshold, The desulfurization apparatus according to claim 4. An oxidation-reduction potential determination method for determining the operating oxidation-reduction potential of an absorption liquid in a desulfurization apparatus having a space inside for desulfurizing combustion exhaust gas containing sulfur and mercury by contact with the absorption liquid, ,
The oxidation-reduction potential determination method includes:
a target value for one of the liquid-phase mercury ratio and the solid-phase mercury ratio in the absorbing liquid;
a predetermined correlation that is a correlation between the mercury ratio and the oxidation-reduction potential of the absorbing liquid;
determining the operating value of the operating redox potential based on and optionally changing the mercury proportion .

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